It is known that compounds which contain positively-polarized chlorine atoms, such as N-chloro compounds, and compounds which contain negatively-polarized chlorine atoms, such as acid chlorides may be reacted together with elimination of chlorine. These reactions generally require high temperatures or even the use of equimolar amounts of Friedel-Crafts catalysts.
One process known in the art, for example, describes the formation of trichloroacetylisocyanate from trichloroacetyl chloride and trichloroisocyanuric acid at a temperature of from 160.degree. to 170.degree.C, (see Zh. Org. Khim. 9 (1973) 1815-18).
It is also known (DAS No. 1,266,288), that carbonyldiisocyanate may be prepared by the thermolysis of N-trichloroisocyanuric acid at a temperature of from 200.degree. to 400.degree.C with simulataneous formation of NCl.sub.3, in accordance with the following equation: ##EQU1##
This reaction is accompanied by said reactions and is difficult to control because of the simultaneous formation of the highly explosive compound, NCl.sub.3.
Another process for preparing CO(NCO).sub.2 is the reaction of difluorophosgene with potassium cyanate in a LiCl/KCl melt at temperatures of about 400.degree.C. This method of preparation involves relatively high technical expenditure because of the low conversion rates obtained and because of high reaction temperatures required, (see Angew. Chem. 79, 860 (1967).